Apparently, I bricked my MBWE…
I really need to find my files back (I'm sure you're surprised by that sentence).

But I have some issues:
First I don't have a sATA controller on my PC, so I just bought a UBS sATA docking station.
…and it's not working. Even if windows can't see linux file system (though I installed software to do so) I think I should be able to at least see the disk

in "disk management" of "computer management", where I could delete the partition if I wanted to format it as a NTFS or FAT drive. But nothing is displayed

there.
In linux, I don't know how to mount the usb drive. However, in /proc/bus/usb/devices I don't see anything that could correspond to the drive.

I'm pretty sure the drives are okay, they're spinning and seeking. I hear them reading files while I turn on MBWE.
For sure, some files must be missing/corrupted and linux cannot boot any more on MBWE.

The disks of 1Tb each where in a raid 1 array. Can my issue be comming from that ? I don't know if a raid 1 disk can afterwards be use as a standalone disk on a non-raid sata controller. In my mind it should be, since a disk is a simple copy of the other one.

Do you think it would be worth to invest in a PCI sATA controller ? I already spend 60€ for nothing with this usb station… :(

just FYI, here's what I did to the MBWE:

I upgraded the firmware, enabled ssh, made it permanent, installed opt and vsftp.
It worked fine, but 3 days later, the smb server was not responding anymore.
So with SSH, witch was working, I rebooted the MBWE. Then nothing.
The blue lights are off all the time.
I hear like if the system is booting and then repeatedly seeking for a file every 10 sec.

That should not be a problem … i have a mybook 500g with only one disk and partition have type dmraid.
I mount them without problem with Linux. I just have to force filesystem as ext3

Ex:
mount -t ext3 /dev/sdb4 /mnt (for the data partition)

Look at the dmesg when pluging your usb adapter, maybe a missing kernel module
You cannot mount ext2/3 partition with windows as partition block size used in the mybook are not compatible
with the ext2 driver of fs-driver.org